Processes for the manufacture of additives are briefly described in the Kirk Othmer Encyclopedia of Chemical Technology, Third Edition, Vol. 22, at page 23, and the description is abundantly referenced. The manufacture of these additives is described in greater detail in Chemical Technology Review, No. 2, 1973, "Lubricant Additives" at Pages 67 through 83, Ranney, Noyes Data Corporation. Manufacturing methods are further described in U.S. Pat. Nos. 2,629,109, 3,861,507 and 4,129,589.
While the various methods of manufacture differ in specifics, they all appear to include mixing a precursor organic acid, such as the higher alkyl benzene sulfonic acid, the higher alkyl naphthenic acid, a higher alkyl salicylic acid or a higher sulfurized alkyl phenol or the alkali metal salt of a selected one of these with a quantity of a base-acting compound of an alkaline earth metal, such as magnesium, calcium, or barium, greatly in excess of the amounts stoichiometrically required to neutralize the acid or metathesize the alkali metal salt. An organic solvent, usually a hydrocarbon, is employed as the reaction medium and an alcohol is commonly added as a promoter. When the process is directed to the production of overbased salts a large stochiometric excess of alkaline earth metal compound is used and carbon dioxide is blown through the total mixture. The reaction product is a slurry of unreacted base acting alkaline earth metal compound in the overbased alkaline earth metal salt product which is dissolved in the reaction medium. This slurry is commonly centrifuged to separate the alkaline earth metal salt product in solution in the reaction medium oil and a centrifugate, which is a thin slurry containing solid unreacted alkaline earth material dispersed in the product and reaction medium.
The centrifugates are opaque liquids having a viscosity comparable to that of the reaction medium and contain large quantities of suspended finely divided hydroxides and carbonates of the alkaline earth metal.